New biostratigraphic data on the Middle-Upper Jurassic (i.e. Callovian-Oxfordian) boundary bed (the socalled:
Arroyofrío Bed), at the South of Zaragoza (NE Iberian Range) show that the Callovian-Oxfordian
boundary is located at the base of this irregular stratigraphic interval. Both the facies and fossil content of the
bed (ammonites, belemnites, brachiopods, bivalves, crinoids, stromatolite structures and planktic foraminifera)
are indicative of marine sedimentary conditions. However, the revision of biostratigraphic data, as well as
taphonomic analysis, confirm the presence of a basin-extent stratigraphic and registratic gap involving at
least the upper Lamberti and Mariae zones. Taphonomic features shown by ammonite internal moulds, such
as disarticulation surfaces, truncation surfaces, phosphate infilling, and in some cases ellipsoidal abrasion
facets and annular furrows, are evidence of taphonomic reelaboration. The latter abrasion features indicate
that ammonite reelaborated moulds stood for long time on the sea bottom after being exhumed and were
abraded by the action of shallow directional currents under extremely shallow intertidal to even supratidal
conditions, resulting in a probable widespread sub aerial exposure of the platform. All this supports the
hypothesis of the boundary bed being formed in punctuated sedimentary events during lower and, most
probably, early middle Oxfordian. These data are of primary importance to understand the palaeogeographic
setting of the northeastern Iberian Platform at the turn of Middle-Upper Jurassic
Thesis Collection
Last Deposit
